Drivetrain loses 4wd vs 2wd.

How much power gets lost in the drivetrain? the most common number ive heard is 10% but i need a source.
How much ekstra gets losts due to the 4WD most have. Is there a big difference between a subarus longitudaly mounted engine vs the transverse mounting of the EVO?

How much power gets lost in the drivetrain? the most common number ive heard is 10% but i need a source.How much ekstra gets losts due to the 4WD most have. Is there a big difference between a subarus longitudaly mounted engine vs the transverse mounting of the EVO?

That is a very good question. The answer will, roughly, be a friction element, and a torque dependent element.

Despite the existence of published test data for driveline losses, very few people seem to have an accurate idea of the numbers involved. Lots of people quote rules of thumb. Even more know even less.

Best guess is 10 percent for each gear set transfering torque.
So a lot more for 4x4, which makes 4x4 useless for F1 even if it was allowed.

In part time 4X4 systems there is usualy extra oil drag and friction from the idling geartrain components not in use.
This drag is also an extra in all the hyped up dual clutch and dual shaft (zero!!!!! joke) shift gearboxes they currently con the general public with. No decent F1 or general racing powertrain engineer would use a dual shaft gearbox or 4x4 if there was an open choice.
Again it is the modern tight restrictive regulations that force all these issues.

WRC's use 4x4 where there is an advantage on loose surfaces where grip is at a premium, however even here if the regs were open, wide specialised tyres on one axle applied to tarmac stages (high grip) would be a better choice.

there was some measurement done for EVO drivetrain and the number was 23%...

That figure needs better explaining, for example is it 23% in comparison to say a 2WD's 20% which makes a 3% difference?

WRC's use 4x4 where there is an advantage on loose surfaces where grip is at a premium, however even here if the regs were open, wide specialised tyres on one axle applied to tarmac stages (high grip) would be a better choice.

Mid to Late Group 'B' proved the worth of a well laid out and devloped AWD on every surface.

Early in Group 'B' the FIA were extremely unfair to Lancia with the 037 (mid engine, RWD), Lancia requested a total tyre width rule rather than a tyre width per axle rule so they could have wider rear tyres offset by narrower fronts but the FIA said no to this logic even though every decent 2WD road sports car in the world is set up like that.

One thing I have read is that some of the power losses calculated from roller dyno vs engine dyno results are simply tyre energy losses because the tyre flexing generates heat.

I believe that this is a big loss on rollers because the tyre is trying to climb the roller all the time. Presumably it is worse for 4WD as twos sets of tyres are being distorted.

We used a wheel free hub dyno system for both 2 and 4x4 dyno runs.We also had a bench dyno.All rolling roads are inacurate.We tried to get the FIA to use our hub dynos to check the power output of F1 cars in the paddock.The teams would not have it.The teams just fit the engines they dont do much development on them, so they are not interested.Aero and marketing is F1 today not technical advance.

Rolling roads cannot be used to work out any proper figures for torque loss.1940s aero engine development was a far higher level of mechanical expertise.

Best guess is 10 percent for each gear set transfering torque.So a lot more for 4x4, which makes 4x4 useless for F1 even if it was allowed.

If we speak about a teoretical F1 car that has 4WD but none of the issues related to aero..

I doubt your claims..

It would dominate every street track.

Canada too.

hell.... with these tilke tracks having hairpin onto straights all the time i bet they would do good there too.

After all. 4WD is illegal in Touring series. even tho they got probably 5-10% less power. and those cars are far from powerfull.Slight OT.Personaly i think 4WD could have been quite entertaining as its not game over once the tail gets a hit by the angry man behind. or in rain.

My dyno man says about 50hp on a normal V8 on a chassis dyno. And the only engine I have had on both seemed to verify that.
Some small engines really struggle on a big set of rollers to actually get them turning.
The discrepancy though between different chassis dynos can be a problem, any back to back testing should be done on the same dyno.
The numbers may not be true but if you show an improvement on the same dyno you should have an improvement.
A chassis dyno does lose a lot through tyre drag as the car is trying to climb out of the rollers, something that can be scarey. Especially as I have seen a building after one escaped!! And never use good race tyres on a dyno as they do tear up.
Engine dynos give more true numbers but a chassis dyno will drag more accentuating problems. And any chassis dyno needs a very good fan to attempt to keep the engine cool. Even for cars with efficient fans on them.

If we speak about a teoretical F1 car that has 4WD but none of the issues related to aero..

I doubt your claims..

It would dominate every street track.

Canada too.

hell.... with these tilke tracks having hairpin onto straights all the time i bet they would do good there too.

After all. 4WD is illegal in Touring series. even tho they got probably 5-10% less power. and those cars are far from powerfull.Slight OT.Personaly i think 4WD could have been quite entertaining as its not game over once the tail gets a hit by the angry man behind. or in rain.

Sure Mat you can make lots of smoke and look real 'cool' at 20, 30 or even 40 mph but that aint F1 cornering by a mile.4x4 does not increase cornering speed it gives better traction on loose surfaces.The same tyre footprint on one axle makes handling better on flat tarmac with less in the way of powertrain losses.4x4 makes no difference or makes worse 'braking and steering control' all else being equal

I read a report some years ago in which I think it was Audi claimed that 4wd actually reduced losses due to rolling resistance, due to less tyre distortion because the same amount of torque required to drive the vehicle at say 80kph was shared amongst 4 rather than only 2 tyres. This doesn't of course take into account increased mechanical losses, but I'm sure they claimed that after taking into account the increased mechanical loss and the decreased rolling resistance, the nett affect was almost insignificant.

I read a report some years ago in which I think it was Audi claimed that 4wd actually reduced losses due to rolling resistance, due to less tyre distortion because the same amount of torque required to drive the vehicle at say 80kph was shared amongst 4 rather than only 2 tyres. This doesn't of course take into account increased mechanical losses, but I'm sure they claimed that after taking into account the increased mechanical loss and the decreased rolling resistance, the nett affect was almost insignificant.

I read that report too, a very long time ago. My own experience bears out the truth of the Audi findings.

I once turboed a front wheel drive Mazda 323, it became pretty fast if not stable road car, but the torque steer was pretty lethal.I then bought the factory 4WD version of the same car, but it was very quickly stolen and written off.

The next step after recovery of the wreck was to fit the entire 4WD mechanicals to the FWD car. So it ended up being the identical car, identical motor, but about 90Kg heaver from the more robust gearbox, and the addition of transfer case, and rear diff.

I was astonished to find it was actually faster and used less fuel than it did front wheel drive.

The hypothesis goes that a driven pair of wheels have far less rolling tire losses than pushing a pair of undriven wheels.What you lose through the mechanical coupling, you gain through some of the weird non linear tire losses caused by rolling tire distortion.

I have also heard stories about Nissan GTRs that were a bit of a disappointment on the dyno, but when road tested, were much faster over the road than expected.

It may be fine to talk about 10% extra mechanical losses from 4WD, but how much power is lost pushing or pulling a pair of un driven wheels along the road ?

In my case, the final proof was a very noticeable gain in fuel economy which has remained over the years, and astoundingly better tire wear.I would not hesitate to recommend 4WD, even if only fuel economy, is the main objective.

I read a report some years ago in which I think it was Audi claimed that 4wd actually reduced losses due to rolling resistance, due to less tyre distortion because the same amount of torque required to drive the vehicle at say 80kph was shared amongst 4 rather than only 2 tyres. This doesn't of course take into account increased mechanical losses, but I'm sure they claimed that after taking into account the increased mechanical loss and the decreased rolling resistance, the nett affect was almost insignificant.

Yes they were pushing that line when they launched the understeering pig Quattro.

Incidentally if you take your trusty torque wrench and measure the torque to turn a diff over, you will know more than 90%(WAG) of the people who quote numbers like 15%.

I wonder if the real questions on 4WD versus 2WD have to include total drive train inertia?

It seems that al 4wd systems weigh more than 2WD, some of that is static parts like an extra dif case etc. but there are fundementally more rotating components in 4WD.

All that extra rotating mas has to be accelerated during car acceleration which requires power. The acceleration may still be superior due to extra traction but it sems logical that more fuel is consumed. In the real world ( hybrids aside) the enrgy put in is absorbed in braking so a net loss.

That figure needs better explaining, for example is it 23% in comparison to say a 2WD's 20% which makes a 3% difference?

that was an actual measurement between a chasis dyno and a engine dyno... However, I think it wasn't done for the sake of people wanting to know the exact drivetrain losses, but rather to have some sort of an idea on crank figures when you use rollers..

I am a big fan of 4wd, and have owned and still own some performance 4wd cars, but I have never seen good fuel economy from them.. Also, in situations where you have lots of grip, you really need a lot of extra HP with a 4wd to be as fast as a 2WD car..

However, real roads, normal tires, and throw in some slip, and 4wd becomes a great asset..

my favorite anecdote was a presentation of a then new renault super hatchback.. the megane rs250 that we organized, and called in some renault clubs to attend. The location was a restaurant on top of a hill, with some test drives planned on local roads used for rallying... I came in, as organizer, with my EVO..

first day..and lots of smart-asses going "yeah, you do not kneed shitty 4wd, good tires and a smart LSD is all you need"

second day

on a more positive note, next day's visitors got a hell of a ride up that hill in the EVO..

How much power gets lost in the drivetrain? the most common number ive heard is 10% but i need a source.How much ekstra gets losts due to the 4WD most have. Is there a big difference between a subarus longitudaly mounted engine vs the transverse mounting of the EVO?

MatsNorway,

The mechanical losses in an automotive drivetrain can vary widely depending upon the type of transmission used, and at what conditions the drivetrain losses are measured.

A good manual transmission can be over 99% efficient, and a good hypoid final drive can be over 98.5% efficient. That would give a total drivetrain efficiency of 97.5%.

Conventional automatic transmissions (with torque converters) have typical efficiencies of between 85% and 96%. Their efficiency is poor at low speed when there is torque converter slip, and the efficiency is better when the torque converter locks up. Conventional AT's tend to produce poor highway fuel mileage due to their parasitic losses from pumps, clutch drag, and windage. For example, if the AT has 4hp worth of parasitic loss at highway driving conditions, and the engine is only producing 32hp to propel the car at those same conditions, the transmission losses alone amount to a 12.5% impact on fuel mileage.

As for the difference between a 2WD and 4WD system, the 4WD system itself would only be less efficient if there were more total gear meshes between the crankshaft and wheels, or if the types of gear meshes were different. Spur and helical gears tend to be very efficient at transmitting power, and a single spur/helical mesh (plus bearings) would have losses of 1% or less. A single hypoid mesh (plus bearings) would have losses of 1.5% or less. All other things being equal, there should be no difference in efficiency between a 2WD and 4WD system since both transfer the same amount of power. (200hp x 0.98) = (100hp x 0.98) + (100hp x 0.98) right?

The orientation of an engine (transverse vs. longitudinal) would only hurt drivetrain efficiency if more gear meshes were required, or if the gear meshes needed to turn corners (ie. using bevel gears instead of spurs/helicals)

I too like 4wd, both proper 4x4 vehicles and AWD cars. None are more economical ever! But are generally more sure footed in inclement conditions. And the AWD cars are far more expensive to maintain!!
Though modern auto 6cyl family hacks are generally more economical both city and highway driving. 4 cylinders though often use more than the 6s!!
And 4wd F1, never. These days all the weight and drag would slow them considerably.

2WD vs 4WD in racing and that discussion will get some pointers at pikes peak in the years coming as the unlimited class is basically open.

Personally i believe that when you don`t limit weight, 2WD is the way to go at the peak.. Dallenbach got my bet.

But if 4WD continues to dominate i consider the discussion almost dead. Audi did after all make 4WD illegal in something as underpowered as Touring car. decpite being possibly 10% down in power. Its not a power loss issue but more down to aero if made legal in F1.

And im not gonna go into a discussion with you Gerrard.. we just end up talking about something called a Wallis that would supposedly take out a Death star with ease... While beeing eco friendly..

For F1 cars drivetrain losses around 5% have been mentioned, but that is with spur gears which are more efficienct than the more common and less noisy helical gears. Power transfer from gear to gear is normally 98-99% efficient or so, but it's not quite that simple as using a constant percentage loss. Some losses in a gearbox are constant, others are speed or load dependant; bearing pre-loads can for instance cause a constant loss. Automatics also have greater losses than conventional manual gearboxes, partly due to the hydraulics involved.

But I would expect a loss of about 8-12% for a two wheel driven car with a bit more for a four wheel driven car. Nissan have quoted a figure just above 10% for their GT-R. Drivetrain losses don't include tire rolling resistance.

Many four wheel driven production cars these days use a simple clutch in the center (Haldex, xDrive and others). With the clutch disengaged all the power goes to either the front wheels or the rear wheels. With the clutch engaging, power will transfer to the normally undriven wheels.

For a F1 car it would be difficult to justify the added weight and aero disadvantage with 4WD, even if it would offer greater low speed acceleration and better braking.

2WD vs 4WD in racing and that discussion will get some pointers at pikes peak in the years coming as the unlimited class is basically open.

Personally i believe that when you don`t limit weight, 2WD is the way to go at the peak.. Dallenbach got my bet.

But if 4WD continues to dominate i consider the discussion almost dead. Audi did after all make 4WD illegal in something as underpowered as Touring car. decpite being possibly 10% down in power. Its not a power loss issue but more down to aero if made legal in F1.

And im not gonna go into a discussion with you Gerrard.. we just end up talking about something called a Wallis that would supposedly take out a Death star with ease... While beeing eco friendly..

the problem at pikes peak now is that it will all be paved next year.. I see the 4WD brigade loosing out..

might be an interesting exercise for Peugeot , now that they have stopped with lemans, to go there with their diesel 908 racer and try for a record.

A good manual transmission can be over 99% efficient, and a good hypoid final drive can be over 98.5% efficient. That would give a total drivetrain efficiency of 97.5%.

We have a transmission expert on this forum and he says 10% loss per gearset. That means 81% efficiency for a typical layshaft RWD manual transmission. You've got a hide coming here and claiming 99%. You'd better stick to aeroplanes.

That is not true in most respects. The term "drivetrain" can encompass lots of components, and the mechanical losses attributable to each component can be the result of different variables. To keep things simple, let's just consider gear and bearing losses.

With gears there are 3 predominate sources of mechanical losses: contact sliding, contact rolling, and windage. For a given gear mesh geometry, and assuming hydrodynamic contact conditions, sliding and rolling losses are mostly a function of transmitted power, not torque. Windage losses are mostly a function of speed (ie. pitch line velocity).

With rolling element bearings, there are 2 significant sources of mechanical losses: viscous losses and friction losses. Viscous losses are mostly a function of bearing rpm. Friction losses are mostly influenced by load, which is ultimately a function of shaft torque in geared systems. Viscous losses in rolling element bearings can be the most problematic issue, since these losses increase approximately to the 5/3 exponent of rpm.

the problem at pikes peak now is that it will all be paved next year.. I see the 4WD brigade loosing out..

Most likely.

might be an interesting exercise for Peugeot , now that they have stopped with lemans, to go there with their diesel 908 racer and try for a record.

Then they need to make a steel rollcage in the car first. they got their own rules for safety. That part of why pikes peak does not get exotic machines from other race classes. And thats why it will live on.

Why carbon tubs is the norm in high level race classes i wonder about.. Carbon casting? is so spesialised and expensive it makes any race field smaller.

When/if KERS becomes big in F1 4WD might return to harness more energy under braking. But as of not its no go due to aero dominance.

Then they need to make a steel rollcage in the car first. they got their own rules for safety. That part of why pikes peak does not get exotic machines from other race classes. And thats why it will live on.

Why carbon tubs is the norm in high level race classes i wonder about.. Carbon casting? is so spesialised and expensive it makes any race field smaller.

When/if KERS becomes big in F1 4WD might return to harness more energy under braking. But as of not its no go due to aero dominance.

Part time 4x4 in F1 for corner handling using front wheel m/g's is a good development direction.Braking using m/g's is not 4x4 drive but a development of energy recovery.

first it was KERS who was fine, then it was MGU and something about termal energy.. and now M/g`s ???

it you mean KERS at the front call it front KERS or just KERS at the front.

And yes having front KERS with diffs and so on at the front is the next step.

Why have front diffs when you can have one motor/generator for each front wheel and only use them for improveing cornering and recovering braking energy.The problem is, that if they do it and go further with other new ideas like I have for energy recovery and mechanical handling (and no I am not explaining any), it will show for definite that all electric is the only sensible way to go for peak performance in the future and the motor heads dont like that at all.As for 'new' words, I take the leed from those who wrongly call modern gearboxes seamless. If BS baffles brains today (because most who read it have little if any practical engineering experience and usualy only have degrees in basket weaving), I will claim the right to BS as well.

Without a 50 percent reduction in downforce any such development (and there is much more) would be totaly masked by aero downforce.
Soon it will be possible to bolt the hubs onto hard chewing gum for what use mechanical set up is worth.

Braking with an electric KERS is not as simple as it seems. There is a limit to the recovery rate possible with a battery electric KERS. So the braking system must continually balance the KERS input and the overall friction brake effort, as well as the brake balance front-to-rear. Not an easy task.

As for a M/G on each wheel, this presents several issues. First, a M/G designed to operate at the speed/torque of an F1 wheel would be very heavy, and would not be practical in terms of unsprung mass. Second, having a separate motor driving each front wheel without an interconnect to synchronize them might create a control issue if one motor fails.

It is difficult to get an electric motor to operate efficiently over the range of speeds needed for any automotive drivetrain application. That's why pure electric cars like the Tesla, still use a geared transmission with their electric propulsion motors.

Having a KERS system on each wheel means having driveshafts to the tub.. Its a given.. for me.

Appart from the gearing issue i doubt all this being very tricky. Im guessing you could simplify things a whole lot and work from there. steering wheel input determines the speed difference allowed for the motors to have etc. Failsafe systems can disconnect the motors in milliseconds.

by checking torque delivery vs requested.

But being competitive in F1 in the near future with similar rules that we have now... No way.

[quote]name='bigleagueslider' date='Feb 16 2012, 07:05' post='5531497']
Braking with an electric KERS is not as simple as it seems. There is a limit to the recovery rate possible with a battery electric KERS. So the braking system must continually balance the KERS input and the overall friction brake effort, as well as the brake balance front-to-rear. Not an easy task.[/quote]

Thats why there needs to be a return to flywheel storage and other ;) and more open regulations for energy recovery. At present F1 is just a control formula.

[quote]As for a M/G on each wheel, this presents several issues. First, a M/G designed to operate at the speed/torque of an F1 wheel would be very heavy, and would not be practical in terms of unsprung mass. Second, having a separate motor driving each front wheel without an interconnect to synchronize them might create a control issue if one motor fails.[/quote]

Not with the dual system I have in mind.

[quote]It is difficult to get an electric motor to operate efficiently over the range of speeds needed for any automotive drivetrain application. That's why pure electric cars like the Tesla, still use a geared transmission with their electric propulsion motors.[/quote]

I have a patented electric shift energy recovery system waiting just for this purpose. That is Kers, Hybrid and full electric.
It is compact, fits a box of some 20cm and is a multi segment motor/generator AND a multi speed gearbox with 'added torque during the shifts.
It is suitable to replace conventional gearboxes with the addition of a control circuit and batteries to convert most current road cars to hybrid.
It allows a much more efficient and compact design for hybrid and range extener vehicles and it will increase the range and efficiency of a full electric vehicle.
Tesla originaly had a three speed gearbox that lasted 2,000 miles they replaced it with a 2 speed, which is as much as a conventional gearbox concept will handle with the flat torque curve. The formulec EV1 built by Mercedese also has a two speed gearbox from Hewland, I was consulted on this one.
That is nowhere near enough either.